28. July 2008
temperatures at karst lakes on Vardeborgsletta, western Spitsbergen
Contact person for additional information: Hanne H. Christiansen
Text and photos by Ole Humlum
lakes on Vardeborgsletta
Vardeborgsletta is located east of
Kapp LinnÚ at the west coast of
Subterraneous drainage of the valley seen in the photo above, July 27, 2004. Water draining from the lakes disappears into the ground at the inland end of the valley.
The local bedrock below this part of
Vardeborgsletta is Permian limestone (290-270 mill. years old), a bedrock type which shows increasing solubility
with decreasing temperature, in contrast to most other bedrock types. It has
therefore been suggested that the valleys and lakes in Vardeborgsletta are karst
phenomena, produced by chemical solution (┼kerman 1980; Salvigsen and Elgersma
1985). The linear valleys itself may indicate the position of active, geological
fault lines parallel to the west coast of
Permafrost is expected to
characterise the area near Kapp LinnÚ, a situation which would tend to hinder
the development of karst phenomena, as most water would be frozen and therefore
not available for chemical processes. Ongoing geological faulting activity, however, may produce enough frictional heat to prohibit the
development of permafrost along the fault lines, keeping ground temperatures
near or above freezing, thereby enabling the presence of unfrozen ground water for
prolonged periods each year. If so, this would make rapid chemical solution of
the limestone possible along the fault lines, with associated development of
karst features like sinkholes and subterraneous drainage.
To investigate the viability of
this hypothesis, at 25 July 2005 two ground temperature profiles were therefore
established on Vardeborgsletta, near the bottom of one of the valleys and on the
undisturbed surface in between valleys, respectively (see photo at top of this
page). Four thermistors were installed in each profile from the surface to about 150 cm depth.
Ground temperatures have since been recorded hourly. The results are shown in
the two diagrams below
Ground temperatures measured in the undisturbed surface near one of the valleys in Vardeborgsletta (see photo at top of this page). The temperature at 145 cm depth is 2-3oC above freezing for only a short period each summer, and presumably indicates the existence of permafrost at slightly greater depth.
Ground temperatures measured near the valley bottom near the place of subterraneous drainage from a row of karst lakes (see photo at top of this page). The temperature at 150 cm depth is 6-8oC above freezing for a long period each summer, and presumably indicates the absence of permafrost at the bottom of the valley.
Our ground temperature measurements
clearly show that the ground is warm near axis of the investigated valley, compared
ground below the undisturbed plateau surface nearby. This potentially makes
chemical solution of limestone below the valley more important than below the
plateau surface between valleys.
We have thus not been able to falsify the hypothesis on local absence of permafrost controlling karst development at Vardeborgsletta, and the idea therefore remains a viable hypothesis. Vardeborgsletta may thus represent a fine example of how deep-seated tectonic processes (faulting) may influence both the distribution and thickness of permafrost and modern landscape development (geomorphology).
O. and Elgersma, A. 1985. Large-scale karst features and open taliks at
Vardeborgsletta, outer Isfjorden,
H.J. 1980. Studies on periglacial geomorphology in